G4WeightWindowAlgorithm.cc

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//
// G4WeightWindowAlgorithm implementation
//
// Author: Michael Dressel (CERN), 2003
// ----------------------------------------------------------------------
#include "G4WeightWindowAlgorithm.hh"
#include "Randomize.hh"

G4WeightWindowAlgorithm::
G4WeightWindowAlgorithm(G4double upperLimitFactor,
                        G4double survivalFactor,
                        G4int maxNumberOfSplits)
  : fUpperLimitFactor(upperLimitFactor),
    fSurvivalFactor(survivalFactor),
    fMaxNumberOfSplits(maxNumberOfSplits)
{
}

G4WeightWindowAlgorithm::~G4WeightWindowAlgorithm()
{
}

G4Nsplit_Weight 
G4WeightWindowAlgorithm::Calculate(G4double init_w,
                                   G4double lowerWeightBound) const
{
  G4double survivalWeight = lowerWeightBound * fSurvivalFactor;
  G4double upperWeight = lowerWeightBound * fUpperLimitFactor;

  // initialize return value for case weight in window
  //
  G4Nsplit_Weight nw;
  nw.fN = 1;
  nw.fW = init_w;

  if (init_w > upperWeight)
  {
    // splitting
    //
    G4double temp_wi_ws = init_w/upperWeight;
    G4int split_i = static_cast<G4int>(temp_wi_ws);
    if(split_i != temp_wi_ws)  { ++split_i; }
    G4double wi_ws = init_w/split_i;

    // values in case integer mode or in csae of double
    // mode and the lower number of splits will be diced
    //
    nw.fN = split_i;
    nw.fW = wi_ws;        

//TB     if (wi_ws <= fMaxNumberOfSplits) {
//TB       if (wi_ws > int_wi_ws) {
//TB         // double mode
//TB         G4double p2 =  wi_ws - int_wi_ws;
//TB         G4double r = G4UniformRand();
//TB         if (r<p2) {
//TB           nw.fN = int_wi_ws + 1;
//TB         }
//TB       }
//TB     }
//TB     else {
//TB       // fMaxNumberOfSplits < wi_ws
//TB       nw.fN = fMaxNumberOfSplits;
//TB       nw.fW = init_w/fMaxNumberOfSplits;
//TB     }

  }
  else if (init_w < lowerWeightBound)  // Russian roulette
  {
    G4double wi_ws = init_w/survivalWeight;
    G4double p = std::max(wi_ws,1./fMaxNumberOfSplits);
    G4double r = G4UniformRand();
    if (r<p)
    {
      nw.fW = init_w/p;
      nw.fN = 1;
    }
    else
    {
      nw.fW = 0;
      nw.fN = 0;
    }
  } 
  // else do nothing

  return nw;
}